Compromised fertility is often caused by problems during the periovulatory transition. Meiotic defects, ovulation failure and poor egg quality all contribute to decreased fertility. Oocyte-granulosa cell communication is very important for fertilization and embryo development. However, the specific paracrine signals and the mechanisms controlled by secreted factors in the follicle are not completely know or understood. The LH surge causes dramatic changes in the cumulus-oocyte complex (COC), including expansion of the cumulus cells and oocyte cytoplasmic and nuclear maturation. Recent evidence strongly supports a role for zinc-mediated processes in the regulation of oocyte maturation and fertilization. Cumulus cells secrete a zinc inhibitory factor (ZIF) that potently suppresses zinc accumulation in the oocyte before ovulation. This product is a novel paracrine signal regulating zinc metabolism in the follicle. The objective of this proposal is the biochemica and proteomic analysis of ZIF produced by cumulus cells. In specific aim 1, we will fractionate cumulus cell secreted products according to apparent molecular weight. Next, all secreted proteins in the fraction containing the highest ZIF activity will be analyzed by a sensitive nano-liquid chromatography mass spectrometry (nano LC MS) method. In aim 2, the effect on oocyte fertility of a preparation of conditioned medium containing high ZIF activity will be tested. Together results from these aims will develop a valuable reagent able to precisely control zinc homeostasis during in vitro maturation/fertilization procedures.